Active Led Status; Staggered Spinup And Activity Indication (Sata Power Pin 11); 3.12.1 Staggered Spinup; 3.12.2 Activity Indication - Western Digital WD15NPVX Technical Reference Manual

Product Features
The Serial ATA revision 2.5 specification requires staggered pins for both the hard drive and drive
receptacles. Staggered pins mate the power signals in the appropriate sequences required for powering
up the hot plugged device. These pins are also specified to handle in excess of the maximum allowed
inrush current that occurs during drive insertion. SATA-compliant devices thus need no further
modification to be hot pluggable and provide the necessary building blocks for a robust hot plug
solution, which typically includes:
Device detection even with power downed receptacles (typical of server applications).
Pre-charging resistors to passively limit inrush current during drive insertion.
Hot plug controllers to actively limit inrush current during drive insertion.
3.11

Active LED Status

The drive supports external LED requirements. It provides an activity LED output which is ON
during command execution and OFF otherwise.
The drive strength of this open Drain Drive Active signal is that it can sink 12mA to 0.4V Max. It is
5V tolerant, meaning that the external LED may be driven from +5V or +3.3V so long as the Host
system provides a series resistor to limit the LED current to the lower of 12mA or the rated operating
current of the LED. As an example with +5V and a 2 volt forward drop across a 10mA LED, a 300
Ohm 5% 1/16W resistor would be suitable. In the case of a 3.3V supply for the same LED, the resistor
would be 130 Ohm 5% 1/16W.
The pin corresponding to P11 shall be used for Active LED.
3.12

Staggered Spinup and Activity Indication (SATA Power Pin 11)

SATA device power connector pin 11 is defined as a means by the host to DISABLE staggered spinup
and it may also be used by the device to provide the host with an activity indication. According to the
SATA II specs, "Staggered Spin-up Disable and Activity Signal shall not be enabled at the same time."

3.12.1 Staggered Spinup

When multiple disks are installed in an enclosure, it is desirable to provide a simple mechanism by
which a subsystem controller can sequence hard drive initialization to minimize the current load
presented during power up. Staggered spinup provides this mechanism by preventing the hard drives
from spinning up until after successful PHY initialization (i.e., after PHY enters DP7:DR_Ready
state).
Staggered spinup is only applicable during initial power-up. If a drive is spun down using ATA
commands—as a result of having been placed in Standby or Sleep power modes, for example—the
drive shall spin up following the rules that govern spinup from low power modes described in ATA/
ATAPI-6 or later.

3.12.2 Activity Indication

The host controller through SATA power pin 11 may access storage device status and activity. The
signal provided by the device for activity indication is a low-voltage low-current signal. It is not suitable
for directly driving an LED. A buffer circuit external to the device must be employed to drive the LED.
The activity signal is based on an open-collector or open-drain active low driver. The device shall
tolerate the activity signal being shorted to ground.
3.13

CacheFlow™

CacheFlow is WD's unique, multi-generation disk caching system. It incorporates read cache with
write cache.
WD designed CacheFlow to obtain maximum performance with today's most popular operating
systems and applications. CacheFlow increases performance over prior caching algorithms by
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